As a vehicle-mounted power distribution board that is mounted to a vehicle and has the function of distributing power from a power supply to various vehicle-mounted electric/electronic components, a board is known that includes a circuit structure including a plurality of bus bars and a control circuit board, and electronic components such as a semiconductor element that are mounted to the circuit structure.
Meanwhile, components such as a semiconductor element tend to generate heat and undergo temperature increase during operation. In particular, in the case of such a substrate that allows a large current to flow therethrough, the generated heat may be transferred through a bus bar and a copper foil serving as the conductive materials, as well as a control circuit board to other components that are likely to be influenced by heat, resulting in a failure in the other components.